This spring I am going to take out my lilac. I'll wait till after it blooms - I'm not crazy - but I've come to think that a lilac is no better than a plastic plant as far as the birds and the bees are concerned.

This is all the fault of Douglas Tallamy, an entomologist (for those without handy dictionaries, that's a bug scientist) at the University of Delaware. I've been reading his book, Bringing Nature Home. I even got to have dinner with Doug when he came to Chicago to talk at a landscape design symposium.

Doug calls lilacs, and lots of other exotic plants, plastic, because our local insects, birds, and butterflies can't take nourishment from them. His story concerns the relationship between local plants and the bugs that evolved with them.

Over the course of thousands of years, insects and plants have co-evolved in relationship. Some insects can only eat the leaves or nectar or fruit of specific plants; some plants have developed chemical qualities that are unappealing to bugs, and some bugs have developed a tolerance for those chemicals. Some birds can only eat certain bugs. Some butterflies depend on particular plants' leaves to feed their larvae. Everything has a niche.

The nursery industry has sold us on exotic plants in part because they're described as disease and pest resistant.
That's because our local fauna can't eat them! The problem is, when we overplant with exotics
(and by exotic, I mean plants that are native to other parts of the world, or even to other parts of our countries we deprive our local insects and birds of food.
When we deprive the insects of food, the birds have less to eat. When we omit plants that feed nestlings, we can plant all the fruit adults can eat, but pretty soon there won't be any adult birds because there won't be food for the baby birds.

You get the idea. The whole food web is interconnected. Plants convert sunlight into food; for that reason ecologists call them 'producers.' Not Darryl Zanuck, but producers nonetheless. Some critters eat only plant food: they are the primary consumers. (Some of those critters, of course, are humans like my vegetarian daughter.) Some - secondary consumers - eat both plant and animal tissue - raccoons, snakes, owls, humans . Some - tertiary consumers - eat only animal tissue - hawks, lions, spiders, foxes. If you remove one layer of the web, you get collapse: take away one of the primary consumers, and the numbers and variety of secondary and tertiary consumers declines. Take away tertiary consumers - aka predators - and you get too many primary and secondary eaters. This has happened with the loss of wolves: we have deer eating our tulips. It's also one of the reasons you don't see defoliated forests. Because there's a diversity of diners in the forest, the creatures who eat leaves are in turn eaten by those who get their energy in a more roundabout way.

This is biological diversity - or biodiversity - 101. All our biological systems are dependent on the full range of life. It's why the endangered species issue is so important: when we lose a species, we not only lose the possibilities that species might offer us selfish humans, we also lose an unknown number of other effects. (Excuse me. I just got distracted by a gorgeous male cardinal on the branch of a Linden outside my window.) Biodiverse systems are stable, productive, resistant to disease and invasive plants (think Kudzu), and provide us with invaluable ecosystem services: oxygen, clean water, healthy soil, recycling, and carbon munching, not to mention their value to our emotional and spiritual well being.

A quick look around us shows us that most of the U.S. is not very biodiverse these days. We've replaced complex ecosystems with monocultures of corn or soy or parking lots, houses, shopping centers, industry, roads, and lawns. Did you ever think of American lawns as monocultures? There are almost twice as many square miles of lawn in the U.S. as there are square miles of road. And they're more or less equally useless as nature. Turfgrass roots are short, so they don't help water percolate into the soil; turfgrass doesn't support much more than slugs; turfgrass tempts us to use chemical fertilizers and weedkillers and to consume fossil fuels in our lawnmowers. I could go on and on.
What we've done is create an unnatural country.

Animals' ability to migrate is seriously impaired by this fragmentation of their habitat. Sure, there's a park here and a park there, but how do you get from onepark to the other to, for example, mate? Birds have trouble finding fresh water and suitable food on their migratory routes. (I just read a really interesting novel called The Echo Maker by Richard Powers that starts out with Sandhill Cranes on the Platte River in Nebraska. I think you'd like it a lot.) And animals can't read! (OK, my cat can read, but only catfood labels.) The bison in Yellowstone don't understand the signs telling them to stay in the park; as a result they're getting shot for trespassing in what has always been their back yard.

OK, I'll spare you the rant. But here's the good news. Gardeners can make a real difference for birds, butterflies, and even other animals by planting native plants in our gardens. Imagine a stretch of suburbs that was friendly to birds: they could get enough food for their nestlings without having to exhaust themselves searching all day every day. Bugs would be numerous, and so would their predators. Butterfly larvae could enjoy milkweed leaves, and later in the season, the mature butterflies could eat from the flowers of other species of milkweed. When we plant exotics, we don't support biodiversity, but when we plant natives, we do.

According to Doug Tallamy's book, if you can only plant one native plant, make it an oak. Generally, trees and shrubs do more for diversity than perennials and annuals, but my mantra is 'something is better than nothing.' In his index he lists the plants that support showy butterflies and moths, and he also has a nice list of native plants for different regions of the country that you can plant to promote biodiversity and invite birds and butterflies into your garden. Ask your library to order the book, and get rid of a boxwood, a lilac, or a forsythia and replace it with a viburnum, a sumac, or a native dogwood.

As an added bonus, your grandkids, if you're lucky enough to have some, will get a huge kick out of the bugs in the garden. Remember the pleasure of being 6 and turning over a rock to find the soil teeming with really cool beetles? We can still have that kind of fun.